The small intestine exerts powerful effects on both gastric secretion and motility which are predominantly inhibitory. This is the so-called "enterogastrone" effect, and appears to be a mixture of autonomic and humoral or hormonal mechanisms. Only a few of these are well delineated. It is proposed to dissect "enterogastrone" by using pure polypeptide hormones compared to endogenous humoral agents with and without ablation of autonomic nerves. In addition to better understanding of gastric physiology, a strong possibility exists that peptic ulcer may represent failure of inhibition in addition to or instead of augmentation of gastric secretion.